You are correct. In theory, if you draw a rectangle that is 0.010" wide, it should measure between 0.017" and 0.020" after factoring in the laser's kerf. However, please note that there are many factors that affect the cutting, so we do not guarantee any particular tolerance.
You should also note that all acrylic/plexiglass materials are infrared transmitting, even opaque colors. For an IR-blocking material, you might consider ABS instead.